Conventionally, an electronic key (portable device) for a vehicle includes a casing body, in which a wireless communication device for a key is mounted, and a lid. This kind of electronic key for a vehicle is required to be downsized to improve portability and is required to be attached with a decorating member to improve design. Japanese Patent No. 3,706,233 discloses an electronic key for a vehicle having a fixation structure (snap fit structure) in which a detachment of a housing and a cover is restricted by elastic deformation of a holding rib including a hook part. In a case where the electronic key has the fixation structure, when a battery in the electronic key needs to be exchanged, the cover can be easily opened by applying a force to a fitting plane of the housing and the cover in a direction opposite from a fitting direction.
As a structure of attaching a decorating member to a casing body and a lid, the decorating member may be put between the casing body and the lid to easily attach the decorating member. However, in the above-described structure, a tolerance in a disassembling direction in not secured. Thus, when a force is applied to the decorating member in a twist direction, the casing body and the lid may be disassembled. In addition, because the decorating member is fixed only when the lid is fitted to the casing body, when the casing body and the lid are disassembled to exchange the battery, the decorating member may fall and may be lost. Furthermore, in a fixation structure in which the decorating member is merely put between the casing body and the lid, a fixing part of the decorating member needs to be large to secure strength of the decorating member. Thus, dimensions of the casing body and the lid need to be increased, and a dimension of the electronic key is likely to be increased.